The Church certainly lays claim to the right to development of doctrine. It is not, however, guilty of creating doctrine out of wholecloth. If the fundamental core of any doctrine cannot be found in the Deposit of Faith, then it cannot be "doctrine" at all.
A good example of this is the prohibition of women in the priesthood. The bottom-line, according to JP II, is that the Church "has no authority" to ordain women, because such an action is not found in the Deposit of Faith: it is not a teaching of the Apostles, nor can it even be "developed" from any teaching of theirs. Certainly, in today's climate, it would be expedient for the Church, at least in the West, to allow women to be ordained. Yet, against popular opinion, the Church steadfastly refuses to do so, on the grounds that it hasn't "authority" in the matter. Those who say or imply that the Church simply makes up stuff as it goes along would do well to consider this modern parable to the contrary!
Most protestants applaud the Catholic Church for sticking to Conservative principle on many things. The core beliefs of Catholics make them brothers in Christ. But Where most Protestants scratch their heads is this nearly religion of Mary that has been created. I am OK if you want to pray for intercession or if you want to display artwork of the virgin Mary. It is Mary is the co-Redeemer that goes to the point of conflicting with the Bible. The Catholic Church takes their Mary doctrine way too far, and even if you want to argue that the official Church position does not cross the line, the doctrine takes many Catholics to the point where they do cross the line into worshiping Mary. And that is how many non-Catholics see it.